Many power banks switch off when the current is low for a while. A sleeping microcontroller can draw less than they expect.
What the message means
The bank decides the phone is fully charged when the current drops below a threshold, and then shuts the output.
Fix it in this order
- Look for a power bank with a low-current or “always on” mode, which is sold for small devices.
- Add a small load resistor or an LED that draws a little more current, if the power budget allows.
- Use a battery pack with a regulator designed for a robot instead.
- Check that a motor start pulse does not trip the bank over-current protection.
- Use a good short cable to cut voltage drop.
Why it happens
Many power banks include an auto-shutoff circuit that watches the output current. When the draw stays below a small threshold for a while, the circuit assumes the device has finished charging and turns the output off. A sleeping microcontroller or a robot at rest can draw very little, so the bank cuts power while the robot is still needed. A sudden high current, such as a motor start, can instead trigger the bank’s over-current protection and shut it down.
The remedy depends on which shutoff is involved. Banks sold with a low-current or always-on mode keep the output live at small loads. A small constant load, such as a resistor or LED, gives the bank enough current to stay on, though it wastes energy. For robots with motors, a battery pack with a regulator and an adequate peak-current rating is the more reliable choice. Check the bank’s datasheet for its cut-off threshold and output rating.
If you see this, do this
| You see | Do this |
|---|---|
| Turns off while idle | Low-current cut-off. |
| Turns off when the motor starts | Over-current trip. |
Confirm the fix
- Read the robot’s idle current draw with a multimeter in series with the load, and note the milliamp figure.
- Connect a resistor or LED load across the output at that idle level and check whether the bank stays on for ten minutes.
- Run the motors while watching the output; if the bank cuts out only at motor start, the over-current trip is the cause.
Common mistake: Readers assume the robot’s electronics are faulty when the power bank is simply shutting off because the load is too small for its shutoff circuit.
Related
robot battery guide, battery sag.
Last reviewed: November 2026. These are the usual causes and the order that finds them fastest. Test on your own board; clones and cables differ.